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>>>then the shock. and now the hard questions. were there warning signs? the question friends of the teen who opened fire in his denver area
high school
on friday are wrestling with tonight. 18-year-old
karlpierson
took his own life after storming into his
high school
and shooting a classmate, severely wounding her. now a friend of the shooter is telling nbc news that
pierson
had grown angry and had made threatening remarks about the teacher who police think was his prime target. nbc's ron mott spoke with a friend today. he joins us from centennial,
colorado
work brand new details on this story. good evening.

>> reporter: hey, lester, good evening to you. a darker image of
karlpierson
is emerging from one of his classmates who said he thought he knew him pretty well. they spoke last monday about
pierson
possibly coming back to the
debate team
. he said he scrunched down in the hallway when the shots rang in the hallway before breaking down when he found out the shooter was his friend,
karlpierson
.

>>my first instinct is to want to defend him but i know that's wrong. it is indefensible, what he did. it is horrible. it is hard to process those emotions.

>>i'm
karlpierson
at
arapahoe high school
.

>> reporter: co-captains on the
debate team
weren't
close friends
but he felt close enough to help him.

>>speech and debate
was his life and the fact he was not there crushed him a little bit. it made him tense and angry.

>> reporter: it had been a stressful fall term for
pierson
. he had grown angry from losing his coveted spot on the team months ago which made the coach, the librarian a wanted man in
pierson
's eyes.

>>karl
and murphy did not get along. whatever it was escalated to a death threat.

>>his intent was evil and his evil intent was to harm multiple individuals.

>> reporter: police say
pierson
stormed into the school heavily armed, prepare to hurt many more than just one person. as he moved toward the library looking for murphy, he shot 17-year-old claire davis in the head point blank, eventually turning the weapon on himself.

>>the
karl
that i knew was a good person but obviously the
karl
that came into school friday was not.

>> reporter: the violence only added to the disbelief and pain in a community especially hard hit by deadly spree killings. columbine in
1999
. 13 dead. a
movie theater
in aurora just last year. another 12. today
colorado
's governor echoed what many have expressed here.

>>what in the world is going on in the denver metro?

>>god only knows. there is no rational explanation for it happening here. i'm sick of it. i've had enough of this. everyone in
colorado
has had enough.

>> reporter: he said he has talked nonstop to classmates on friday hoping to make sure no one internalizes the trauma when help is all around.

>>i did try to help him and i didn't get to him. and other people tried to help him and didn't get to him. and i think there are so many people in my school that were supportive of him but no one was able to get to him. at the
end of the day
, that's what happened.

>> reporter: joel said he talked to a number of students and a number of students have gone into what he calls a shell. he is encouraging everyone to talk to counsellors and one another. in the two days since it happened, he said it has really helped him.